Optimized ore processing using molten salts for leaching and thermal energy source

ABSTRACT

A method for the electrolytic production of pure copper from copper-containing compounds dissolved in a high-temperature bath of molten salts which function as an electrolyte in an electrolytic cell. An electric current is passed between an anode immersed in the copper-ion rich molten salt bath and a cathode or cathode-lined kettle in which the molten salt bath is contained, thereby reducing the dissolved copper ions to form pure molten copper. The deposited molten copper collects at the bottom of the kettle and can be separated from the molten salt bath using conventional means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.14/847,068 filed Sep. 8, 2015 all teachings of which are incorporatedherein by reference thereto.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments described herein generally relate to the electrolyticextraction of pure metals from metal-containing compounds. Moreparticularly, the present invention relates to the electrolyticproduction of pure copper in two phases. In the first phase, copper ionsare extracted from copper-containing compounds such as copper ore,concentrated copper, and slag using a high-temperature bath of moltenchloride salts in the presence of oxygen. In the second phase, anelectric current is passed between an anode immersed in the copper-ionrich molten salt bath and a cathode kettle in which the molten salt bathis contained, thereby reducing the dissolved copper ions to form puremolten copper. Because the density of molten copper is higher than thatof the salts which make up the molten salt bath, the deposited moltencopper collects at the bottom of the kettle and can be separated fromthe molten salt bath using conventional means.

This method has been tested for copper extraction and electrodeposition,but is believed to be equally applicable to the extraction of any metalwhose formal reduction potential is more positive than the most noblemetal ion in a molten chloride salt (e.g., in a molten salt comprised ofNaCl/KCl/ZnCl₂, the most noble metal ion is Zn⁺², which has a reductionpotential of −0.76 V versus NEE) and less than the reduction potentialof oxygen, the most aggressive oxidant in air, whose reduction potentialis 1.23 V versus NHE. Among the clearly desirable metals that can beextracted using the claimed method are gold, silver, copper, nickel,etc.

Description of Related Art

Conventional metal mining operations, such as for copper, silver, andgold, have the primary purpose of extracting pure metals from metallicore. Naturally occurring copper is present in various ionic forms, suchas copper sulfide (CuS), copper oxide (CuO), and copper chloride(CuCl₂). In conventional methods, the copper ore is usually treated withchemicals to dissolve ionic copper in an aqueous solution which is thentreated with reducing agents to yield metallic copper.

The most effective conventional copper extraction methods take place inan aqueous solution and combine ion-exchange and solvent-extractionprocesses, which can be broken down into four principal stages:

Leaching (L): In this step, copper ions are removed from the ore usingchemical agents called lixiviants, typically a solution of sulfuricacid. When the lixiviant is applied to the ore, it dissolves the copperions to yield a pregnant leach solution (PLS).

Ion Exchange (IX): In this step, the copper containing PLS is passedthrough a resin in columns, and copper is adsorbed on the resin. Thecolumn is then regenerated with sulfuric acid solution, which yields arelatively impure copper sulfate solution (electrolyte), suitable forfurther treatment through the solvent extraction process.

Solvent Exchange (SX): In this step, an organic extractant thatselectively binds copper but not other impurities is dissolved in anorganic solvent (diluent) and is mixed with the copper-containingaqueous solution. The copper-loaded organic solution is separated fromthe impurities in the aqueous solution in a settler tank. The barrenaqueous solution, called raffinate, is sent back to the leaching-ionexchange process for reuse. Sulfuric acid solution, comprising mostlyspent electrolyte returned from the electro-winning process is thenadded to the loaded organic mixture, which strips the copper into ahighly purified aqueous copper sulfate electrolytic solution ready forelectrowinning.

Electrowinning (EW): In the final step, electrolysis of a pregnantcopper sulfate electrolyte solution, produced in the solvent extractionstep above, takes place and copper ions in solution are plated(electrolytically deposited) as copper metal onto a cathode.

A well-known conventional copper extraction process is typified by theCominco Engineering Services Ltd. (CESL) process. In this process, ahypothetical refinery produces 154,000 tpy Cu from 550,000 tpyconcentrate containing 29% Cu and 9 g/t Au. For this hypotheticalscenario, preliminary operating costs for the gold/silver process areestimated to add about US$ 0.024/lb Cu to the existing CESL copperprocess, for a total of US$ 0.20/lb Cu. The net cash flow is improved byapproximately US$ 74 Million per year, compared to the alternative ofselling the concentrate to a smelter and paying realization costs. Thisis equivalent to US$ 0.22/lb Cu increased cash flow, before amortizationcosts.

Metallic gold and silver can also be recovered from copper sulfideconcentrates using cyanide to leach residue from existing copperprocesses. This process was developed as a hydrometallurgicalalternative to smelting and refining, and consists of five main processsteps (described above):

1. Pressure oxidation of concentrate at ‘medium temperature,’ i.e.,above the melting point of sulfur, (T>116° C.) but below phasetransition point (160° C.) of sulfur;

2. Copper leaching of the solid oxidation product with raffinate atatmospheric conditions to produce a Pregnant Leach Solution (PLS);

3. Solvent extraction of PLS to produce a high purity electrolyte andregenerate raffinate;

4. Partial neutralization of raffinate to remove any excess sulfate; and

5. Electrowinning to recover copper in commercial product form (fullcathodes).

Copper, gold and silver recovery by simple cyanidation of the resultingresidue is unsatisfactory as it consumes very large amounts of cyanide,due to formation of both thiocyanate and also copper cyanides, typicallyconsuming >30 kg NaCN/ton residue. Cyanide consumption can be reduced tolower levels by a combination of new processing improvements, whichinclude pressure cyanidation for short retention times to minimizethiocyanate formation, partial suppression of copper cyanide formation,and finally by recovering cyanide as efficiently as possible from the(reduced) copper cyanide complexes. Total cyanide consumption with theimproved cyanide processing can be reduced to approximately 2 kgNaCN/ton of concentrate. Using this method, gold and silver recovery ofapproximately 90% can be achieved. However, this extra processing addsextra complexity, time and labor. The cyanide consumption due tothiocyanate is between 0.5-1.3 kg NaCN/ton residue (slag). This accountsfor about half of the known cyanide consumption. This low cyanideconsumption is the most efficient of the known conventional methods ofprocessing of copper/gold/silver concentrates in competition withconventional smelters.

In this process, the copper residue contains two components, residualcopper and sulfur, which tend to consume very large amounts of cyanideif the residue is further processed. When the residue is leached under“standard” conditions, i.e. leaching with low concentration cyanidesolution in atmospheric conditions for 1-3 days. The residue still has asignificant copper content, despite the fact that it has already beenprocessed specifically for copper extraction. Since extraction is about95-98% efficient for Cu, the residue typically contains 1.0-1.5% Cu.This small Cu content is partly (15-25%) soluble in standard cyanideleach conditions, leading to the formation of soluble copper cyanidecompounds, as well as other cyanide compounds such as cyanate. Alsopresent in the copper residue is elemental sulfur that typicallyconstitutes 25-35% of the residue. A minor amount of elemental sulfuralso reacts with cyanide solutions leading to the formation ofthiocyanate compounds. Both of these phenomena lead to very high cyanideconsumption when the copper residue is treated in a standard cyanideleach, e.g. 30 kg NaCN consumed per ton of copper residue, or more than100× the consumption typically experienced in leaching gold ores. Suchlevels of cyanide consumption render the process far too expensive inview of the modest value of gold and silver to be extracted. Worsestill, the gold and silver themselves cannot easily be extracted fromthe Cu process residue by cyanide leach solutions, and extractions ofgold and silver from leach residue are generally incomplete.

In summary, with standard cyanide leaching of the copper residue, costsare high, gold and silver recoveries are poor, and the costs of theprocess tend to outweigh the value of the recovered metals. Efforts toovercome these difficulties have been devised to reduce cyanideconsumption and boost metal recovery. This process is fairly complex,involving a number of steps and still uses cyanide and sulfuric acid,which are hazardous and toxic if they escape into the environment. Onthe other hand, in aerobic molten chloride salts, gold silver and copperare readily extracted. Gold has a reduction potential of 0.99 voltversus SHE. Where SHE is defined as the Standard Hydrogen Electrodewhose potential is defined as 0 volts and is the reference potential forall reduction potentials and where SHE is associated with the reductionof proton to hydrogen in 1 normal acid solution. Silver has a reductionpotential of 0.8 volt and copper 0.34 volt. The metal most resistant toextraction is gold with a potential of 0.99 volt versus SHE which is0.23 volts low than the reduction potential of oxygen, whose potentialis 1.23 volt versus SHE. Still oxygen having 0.24 volt higher reductionpotential than gold allows oxygen to dissolve gold metal into chloridesalt melt. Ordinarily gold has a standard reduction potential of 1.5volt versus SHE (for Au³⁺+3 e⁻→Au metal). However in chloride salt therelevant gold reduction (and gold metal oxidation) process is AuCl₄ ⁻+3e⁻→Au metal+4 Cl⁻. Clearly due to the shift of gold reduction potentialbelow oxygen reduction, even gold can be extracted when gold ore is inin molten chloride salts. Silver and copper, which in pure form alreadyhad low formal reduction potentials than oxygen (Ag 0.8 volt, Cu 0.34volt), experience a negative shift in molten chloride salt (Ag 0.2 volt,Cu<0 volt), which makes them even easier to extract when in silver andcopper ores are treated in aerobic molten chloride salts. The extractedmetals can be selectively plated one by one by controlling the potentialof the plating process (0.9 for plating Au metal, 0.1 for Ag and finally<0 volt for Cu). In summary gold, silver and copper metal can all bedissolved as chloride salts allowing metal extraction from theirrespective ores, and then these chloride salts can be simultaneouslyplated at high reduction potentials (<0 volt) or selectively plated oneat a time by controlling the reduction potential of the plating bath tothe a specific reduction potential for each specific metal. Metalextraction and deposition from metal rich earths is accomplished usingrelatively benign aerobic molten chloride salt and graphite electrodes,and no other chemical or solvents which have been problematic in thepast due to waste of water, energy, desired metal and hazardous to theenvironment. The metal deposition process from molten chloride salt ispresently targeted to commodity and precious metal but the process isgeneral. For example, using the proper molten chloride (like andaluminum based molten chloride) and silicon chlorides (like Si₂Cl₆) andsubstrates, then high valued semiconducting silicon can be deposited inpolycrystalline and single crystalline forms in a simple reactor usingvery low energy and virtually no waste nor emission of toxic wastes.

Aluminum Production (Hall-Heroult Process) as a Model for CopperProduction in Molten Salts

Aluminum production is a well-known process and consists of miningbauxite ore, and extracting the naturally-occurring aluminum oxides[Al(OH)₃, bohemite γ-AlO(OH), and diaspore α-AlO(OH) which can simply bedesignated Al₂O₃ or alumina] in the bauxite using the Bayer process. Forthe Bayer process, a large amount of heat (steam) is required that istypically produced with boilers or steam from co-generation plants.Approximately two tons of bauxite ore will produce one ton of alumina(Al₂O₃). The alumina can then be transported to an aluminum smelter tobe extracted via the Hall-Heroult process. Approximately two tons ofalumina will produce one ton of aluminum.

In the Hall-Heroult process, aluminum oxides (Al₂O₃) are dissolved in amolten fluoride salt (cryolite, Na₃AlF₆) bath contained in acarbon-cathode lined electrolytic cell that is maintained atapproximately 1000° C. A low voltage direct current passes from carbonanodes immersed in the molten salt bath to the carbon-cathode celllining, causing liquid aluminum metal to be deposited at the cathode,while the oxygen from the alumina combines with carbon from the anode toproduce carbon dioxide. As the electrolytic reaction proceeds, aluminum,which is slightly denser than the electrolyte solution, is continuouslydeposited in a metal pool at the bottom of the cell where it can becollected using conventional means such as a siphon. In addition to CO₂,the cell also produces hydrogen fluoride from the cryolite and fluxwhich are either treated or vented into the atmosphere.

In an analogous process, metals and metal ions in copper rich earths andconcentrates can be dissolved in oxygenated molten chloride saltsforming metal chlorides at 500° C. which can then be plated directlyfrom the molten salt on a cathode with virtually 100% extraction andplating efficiency. Generally, all metal is recovered at one high overpotential (i.e., at a potential more cathodic than the reductionpotential of the least noble metal), but a specific metal can beseparated by selectively plating at a specific cathode potential ifdesired.

Electrochemically, the extraction and purification of copper bydissolving copper oxide-containing ore or slag or copper-sulfideconcentrate in a molten chloride salt bath and plating the metal incarbon vessels is similar to the process used to make aluminum metal.However, it is believed these methods of aluminum-making have notheretofore been applied to the extraction of metallic copper and otherdesirable metals, for several reasons. Moreover, each intermediate stepin the copper extraction process is less costly, moreenvironmentally-friendly, and safer than the corresponding step in theHall-Heroult Process.

For example, the electrolyte solution consists of inexpensive,recyclable chloride salts (<$1 per kilogram) rather than consumedfluoride salts in the Hall-Heroult Process. Additionally, aluminiumoxide has such a high heat of formation (Al₂O₃=−1675.7 kJ/mol) that allthe water introduced in the bauxite clay has to be removed during thebauxite preparation for the refining process, which adds cost. This costis not incurred in the analogous copper metal plating because copperoxide has a relatively much lower heat of formation (CuO=−157.3kJ/moland Cu₂O=−168.6 kJ/mol), so copper metal does not readily combine withwater to reform copper oxide. If the removal of water is desired thenthis can easily be done if excess heat (steam) is available, which couldcome from the using the molten salt to transfer heat from slag to therefining reactor or using a cogeneration power plant if the fuel cost islow. Finally, the reduction potential of copper is over 2 volts morepositive than the reduction potential of aluminum, so theelectrodeposition of carbon is thermodynamically favored relative tothat of aluminum, meaning that less electricity and cost is required toextract copper. In fact, the yield of copper from ore has recently beenfound at the University of Arizona to be virtually 100% of theoreticalyield.

Objects of the Present Invention

An object of the present invention is to provide an optimized method andapparatus suitable for large-scale, environmentally-friendly processingof copper ore, copper sulfide concentrates, or even slag using a moltensalt bath to produce a highly purified copper cathode product viaelectrolytic deposition.

A further object of the present invention is to provide a method andapparatus for the extraction of metallic copper which is economical inoperation and construction, and which does not require the use of highlytoxic chemicals such as cyanide and sulfuric acid.

A further object of the present invention is to provide a method andapparatus for optimizing the extraction of copper and other desiredmetals by employing a reference electrode to monitor and control boththe initial ionization of copper in the molten salt bath and theelectrolytic deposition of desired metals at the cathode.

SUMMARY OF THE INVENTION

The present invention relates to the electrolytic production of purecopper in two phases. In the first phase, copper ions (Cu⁺ and Cu⁺²) areextracted from copper-containing compounds such as copper ore,concentrated copper, and even slag using a high-temperature (i.e.,greater than 500 to as high as 1085° C.) bath of molten chloride saltsin the presence of oxygen and water from air. In the second phase, anelectric current is passed between an anode immersed in the copper-ionrich molten salt bath and a cathode or cathode-lined kettle in which themolten salt bath is contained, thereby reducing the dissolved copperions to form pure molten copper at temperatures ≥1085° C. Because thedensity of molten copper is higher than that of the salts and earthsthat contained the copper which make up the molten salt bath, thedeposited molten copper collects at the bottom of the kettle and can beseparated from the molten salt bath using conventional means.

According to the present invention, there is provided an apparatus forthe extraction of metallic copper from copper-containing compounds,comprising: a high-temperature, corrosion resistant vessel (preferablyof graphite or other carbon material) in communication with a cathode inan electrical circuit; a molten salt bath comprising one or morechloride salts which functions as an electrolyte solution in theelectrical circuit; an anode (preferably of graphite or other carbonmaterial) immersed in the molten salt bath; a direct current (DC)electrical supply; and a conventional means of separating the puremolten copper electrodeposited at the cathode from the molten salt bath.The cathode or cathode-lined vessel is filled with the metal ion richmolten salt bath.

The molten salts or ionic liquids used in the present disclosure have avery low vapor pressure, such as between about two pounds per squareinch gauge (2 psig) at an operating temperature of 500 degrees Celsiusto about ½ atmosphere (i.e. 7 psig) or less at 800 degrees Celsius to 1atmosphere or less at temperatures as high as 1400 degrees Celsius. Thesalts also have low temperatures of melting (i.e. will transition from asolid to a liquid phase, as low as 200 degrees Celsius and as high as450 degrees Celsius). The salts are aerated (i.e. exposed to air in anopen container) to dissolve the oxygen and water from air into themolten salts or ionic liquid to form a mixture which extracts all metaland metal ions in the ore or slag into the salt as ionic metalchlorides. The metal and metal oxides are unstable and dissolve in theaerated molten halide salt by the process in which metals and metal ionsare transformed to metal halides, which in turn can then beelectrodeposited on a cathode in the same pot as metals.

Not only is the refining of copper in molten salts much safer and moreenvironmentally benign than aluminum-making using molten fluoride salts,but the claimed apparatus and process achieves significant advantagesover conventional means of refining copper and other metals using waterand toxic solvents including sulfuric acid and cyanides. In one or moreembodiments, such as for small scale operations, the extraction andelectrodeposition steps occur sequentially in the same vessel (e.g.crucible, pot, kettle, container, etc.). Additionally, the presentdisclosure covers large scale mining operations where the metalextraction and electrodeposition are conducted in close proximity toeach other, but in separate vessels, or collocated at the same facility.

It is also possible to recycle heat using the chlorides as the moltenchloride salts being used to extract and plate copper were originallydeveloped at the University of Arizona as heat transfer fluids forconcentrating solar power for electrical power generation. Molten saltsand ionic liquids can be very useful heat carriers for recoveringthermal energy from slags. This last development is due to the fact thatat the high temperature (up to 1300 degrees Celsius) these kinds ofliquid salts can operate as heat transfer fluids, whereas no other knownconventional heat carrier can work at such temperatures, e.g. slag isabout 1650 degrees Celsius and thus conventional methods of metalextraction using acids, bases or cyanides on slag do not work, andnon-molten salts would not work with slag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a schematic depicting one embodiment of the system andprocess of the present disclosure.

FIG. 2. is a flowchart of the process steps of the present invention.

FIG. 3 illustrates a schematic of the process steps described hereinusing molten salts as the low vapor pressure liquid, and using a heatexchanger to store and provide thermal heat.

FIG. 4. is a schematic diagram of a pilot plant for extracting metal ioninto molten salt and electrodeposition of metal from the metal ionsdissolved in molten salt.

DESCRIPTION OF THE INVENTION

The foregoing objects of the present invention are accomplished and theproblems and shortcomings associated with the prior art, techniques andapproaches are overcome by the present invention as described below inthe following non-limiting embodiments.

The invention includes an electrolytic cell for the production of copperfrom copper-containing compounds dissolved in a molten salt electrolyte.Preferably, the molten electrolyte is maintained at a temperature ofbetween 500° C. and 1200° C. The copper-containing compounds can beadded to the cell as a batch or on a continuous basis. The electrolyticcell employs anodes and cathodes, the cathode being in communicationwith the vessel containing the molten salt electrolyte. In the processof the invention, electric current is passed from the anode through themolten electrolyte to the cathode, reducing the ionic copper dissolvedin the electrolyte and depositing metallic copper at the cathode.

The electrolytic cell of the present invention employs electrolytescomprised of molten halide salts, preferably chloride salts of alkalimetals and/or alkaline earth metals. In other preferable embodiments,the molten salt electrolyte may comprise NaCl—KCl—ZnCl₂ orNaCl—KCl—AlCl₄ in several eutectic compositions, including withoutlimitation 2-aluminum and 3-magnesium chlorides mixed with Na and Kchlorides, and 4-stable ionic liquids with various cations and chlorideanions. In one embodiment, the electrolyte is composed of a 50:50(mole-to-mole) mixture of NaCl and KCl salts, or 50:50 (mole-to-mole)mixture of MgCl₂ and KCl salts, or other suitable mixtures of moltensalts known and used by those of ordinary skill in the art.

One-Pot System and Process

One or more embodiments of the present disclosure comprise a container,in a one-pot metal extraction and electrodeposition apparatus. Theapparatus, or system, comprises: 1) a high temperature resistant,corrosion resistant outer crucible, wherein the outer crucible comprisesnon-porous glassy carbon material, or non-porous ceramic-filled graphiteor quartz or a nonporous ceramic material; 2) a high temperatureresistant, corrosion resistant inner crucible centered within a bottomof the outer crucible, wherein the inner crucible is cathodic (i.e.functions as a cathode in an electric circuit), and the inner cruciblecomprises porous graphite or non-porous glassy carbon material or anon-porous ceramic-filled graphite; 3) a molten salt within the innercrucible produced by combining a low melting aerated chloride salt andmetal ore or slag; 4) an anode rod positioned vertically within theinner crucible; 5) a power supply operatively connected to the innercrucible cathode and the anode rod; and, 6) a means to stir forcontinuously mixing the molten salt and slag/ore within the innercrucible.

This one-pot method has been tested for copper extraction andelectrodeposition but should work for any metal whose formal reductionpotential is more positive than the reduction potential of the mostnoble metal ion in a molten chloride salt (for example, in NaCl KClZnCl₂, it is the reduction potential of zinc, which is −0.76 V versusNHE) and less than the reduction potential of oxygen, the mostaggressive oxidant in air, whose reduction potential is 1.2 V versusNHE. Clearly desirable metals can be processed including gold, silver,nickel, etc.

Multi-Crucible System and Process

Various embodiments of the present disclosure also compriseenvironmentally friendly processes for extracting and depositing metalsfrom ore and/or slag, while using a plurality of crucibles, vessels,reactors, containers, etc. The multi-crucible system and process issuitable for full scale manufacturing operations that extract anddeposit large quantities of metal from ore and/or slag.

The various embodiments of the multi-crucible system comprise thefollowing components: a mixing crucible able to heat and dissolve metalin slag and/or ore that is aerobically mixed with a low vapor-pressuremolten salts or ionic liquid; a mechanism to remove the undissolved slagor ore from the mixture (e.g. by filtration or decanting); anelectro-chemical reactor able to conduct electro-deposition to removethe pure metal from the liquid solution by depositing it on a cathodeelectrode.

The electro-chemical reactor comprises: a high temperature resistantcrucible storing the liquid solution; a cathode electrode and an anodeelectrode (e.g. graphite) connected to a direct current power supply onan upper end, and immersed in the liquid solution on a bottom end; and,one or more valves to drain the electrified liquid solution from thereactor crucible and into a movable re-cycle tank.

The movable re-cycle tank is able to first receive dense metal (e.g.copper) and then be replaced by an empty tank for receiving themetal-depleted electrified liquid solution comprising molten salts orionic liquid, which can then be used to transport the electrified liquidsalt solution back to the mixing crucible and/or a heat exchanger unit.In an embodiment, the re-cycle tank is heat and liquid sealed to preventsignificant loss of heat and the used liquid solution.

Heat Recycling

In an embodiment of the invention, it is also possible to recycle heatusing the chlorides as the molten chloride salts being used to extractand plate copper were originally developed at the University of Arizonaas heat transfer fluids for concentrating solar power for electricalpower generation. During the copper making process which occurs inmolten chloride salt, copper-depleted, deoxygenated and dehydratedmolten chloride salt or fresh deoxygenated and dehydrated moltenchloride salt can be stored in a tank and passed through pipes whereheaps of hot ground copper earth, concentrates or slag are stored inorder to extract heat from the heaps. The salt needs to be deoxygenatedand dehydrated only if metal tanks and pipes are used. For example ifgraphite, or clay filled graphite, pipes and containers are used, thesalt need not be deoxygenated and dehydrated.

One scenario illustrating the use of the heat exchanger is the fact thatcan be extracted from a slag heap piled into a closed bucket with a heatcollecting tube containing molten salt and passing through the hot slagheap. Collecting heat into the collecting tube is just like the heatcollecting tube used to collect heat from sun shining on a pipecontaining molten salt in a plant for concentrating solar power. Theslag can stay in the bucket until most of the usable heat is sent intothe molten salt to make electricity. That is, the freshly heated moltensalt can go to a heat exchanger, in a steam generator, to make steam to,in turn, make electricity for electroplating copper or for providingelectrical power in the plant or even nearby residential housing.Instead of sending the heated molten salt to the steam generator, theheated molten salt can fill a graphite kettle which is used to processslag or ore.

The molten salt in the slag or ore is used to dissolve metals in themolten salt, and after metal ions are dissolved, the metal ions areelectroplated at temperatures over the melting point of metal (e.g.,1,984° F. or 1,085° C. for copper), causing the liquid metal sinks tothe bottom of the kettle, which can then be poured out of the kettle bymeans of a drain. When most of the desired heat is transferred from theslag to the salt for whatever reason, then the slag can be dropped intothe graphite kettle by opening the bottom of the bucket so slag passesthrough the pipe into the graphite kettle for processing into coppermetal and then new hot slag is put into the bucket and the whole processis started again.

Any heat not used to make electricity for making copper ions to coppermetal can be used to make electricity for factories and houses in nearbyareas. Two hundred and fifty (250) megawatts is enough electricity for70,000 households. So the huge amounts of waste heat in copper heaps canbe used to make commercial amounts of electricity. Any of the heat inthe molten salt which is not extracted from the heat exchanger can bestored as hot salt in tanks and the stored energy can be extracted forheating the smelter process(s) or sent to a steam generator for makingelectricity on demand.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is further illustrated with reference to theaccompanying drawings, throughout which reference numbers indicatecorresponding parts in the various figures. These reference numbers areshown in parentheses in the following detailed description.

Referring to FIG. 1, there is shown a schematic drawing of oneembodiment of the system and process of the present disclosure. Metalore and/or slag 110 (e.g. comprising copper, gold, silver, or anycombinations thereof) is added to and stirred in crucible 120 whichcontains high temperature, molten salt (MS) or ionic liquid (IL)recycled from tank 150. The crucible 120 is exposed to air, meaning thatthe top of the crucible remains uncovered, or that air is stirred intothe liquid solution. In an embodiment, the molten salt comprises sodiumchloride and potassium chloride and zinc chloride eutectic (i.e.NaCL-KCl—ZnCl₂), in a mixture of a 0.5 to 0.5 to 1 molar ratio,respectively. This NaCl—KCl—ZnCl₂ molten salt melts at about 200° C. andhas very low vapor pressure (7 psig) and is chemically stable to over1000° C. in air.

The ore or slag is added to crucible 120 via standard machinery known inthe art, such as via a crane or conveyer belt. The re-used molten saltsor ionic liquids may be pumped or poured into the crucible 120 from there-cycle tank 150.

Heat is applied to the crucible 120 while the metal from ore or slag isdissolved into the molten salt or into the ionic liquid, and the mixtureis stirred to dissolve the metal ore or slag. This will produce a liquidsolution containing a metal chloride (e.g. CuCl₂). The appropriatetemperature range for the applied heat is about five hundred to elevenhundred degrees Celsius, although other temperatures are envisionedwithin the scope of the present disclosure and are a function of thetype of molten salt or ionic liquid used and the metal being extracted.The source of the heat 130 may be melted slag from ore smelters (e.g. upto 1650 degrees Celsius) and/or standard heat generatingelectro-mechanical devices known by one of skill in the art.

In one embodiment (as shown in FIG. 1), the liquid solution is passedthrough a filter 140 by gravity or a vacuum pump 170. Excess slagresidue is discarded by inverting the crucible by using, e.g., a craneor other mechanical method. The remaining solution enters a crucible 106which is subjected to heat via source 132. Crucible 106 comprises a pairof electrodes 108 (anode) and 109 (cathode). Crucible 106 furthercomprises a pressure release mechanism 105 as a safety mechanism forwhen the pressure becomes too high within the crucible. Crucible 106further comprises a valve 107 to first drain the molten metal into arecycling tank 150 and then to drain the used metal depleted molten saltor ionic liquid into the tank 150. The used, heated molten salt in therecycling tank is then transported back to and added into the stirringcrucible 120, via for example the use of a crane. One of skill in theart would readily know of mechanisms to transfer used molten salt orionic liquid from tank 150 to crucible 120 (e.g. automated railmovement, vehicle operated by driver, etc.). Thus the hot molten salt isre-cycled to reduce operating cost for materials and for heating.

During the metal plating step a variety of types of electrodes 108, 109can be used, (e.g. graphite, glassy carbon, or any stable refractorymetal). Metal forms on graphite cathode 109. As metal forms on thecathode 109, the graphite anode 108 will oxidize to carbon dioxide dueto the presence of trace water in the molten salt in contact with air.

Referring to FIG. 2, there is shown a summary of the general steps ofthe metal leaching process using low vapor pressure, aerated moltensalts or ionic liquids of the various embodiments disclosed herein, andFIG. 3 is one exemplary embodiment of FIG. 2. The vessel furthercomprises a bottom and walls extending upward from said bottom. Theopening formed by the top of the vessel walls is exposed to air, and thevessel is optionally configured with a mechanical stirrer. In operation,the mixture of molten electrolyte and metal-ion rich material is stirredto aerate the mixture of molten electrolyte salt and metal-ion richmaterial, thereby causing metal ions to dissolve in the electrolyte.

In step 210, the metal ore or slag is mixed with the low vapor-pressuremolten salt or ionic liquid to form a mixture. The mixture is aerated,via for example having the crucible not be covered. The crucible istemperature controlled to enable all metal and metal oxides to beextracted from the ore or slag, and to form metal ions which aredissolved in the liquid solution in the mixture.

In step 220, the liquid solution with the metal ions is separated fromthe metal depleted solid ore or slag by filtration or decanting (pouringoff from a level just above the metal depleted solid), or otherindustrial separation process. The metal depleted solid can be dumped atthis point, for example by inverting the vessel, which can then bereused to transfer heat to a new liquid solution of metal rich ore orslag and molten salts or ionic liquid.

In step 230, the metal-rich hot liquid solution is put into anelectrochemical reactor for electrodeposition. At this step the very hotliquid (about or above 1000° C.) can be passed in a metal tube from thepot (heat exchanger to a water bath) and the cooled (500° C.) liquidback to a graphite pot which acts as a cathode to make metal. Theexchanged heat can be used to make steam from water to drive a turbinegenerator to make electricity.

In step 240, metal ions from the liquid solution are electrodeposited aspure metal at a carbon cathode while carbon dioxide forms at a carbonanode using an electrical current.

The metal is denser than the salt and can be poured out from the bottomof the reaction vessel (like a graphite crucible) while metal-depletedlow vapor-pressure liquid remaining on top in the electrochemicalreactor may then be recycled to the initial step for again extractingmetal from ore or slag.

Referring now to FIG. 3, there is shown a schematic chart of anexemplary embodiment of a method and system for extracting metal ioninto molten salt (e.g. leaching metals from slags using molten salts).The heat from the hot melted slag 305 passes through a heat exchanger315. The heat exchanger 315 provides heat to the molten salt and thislast hot salt is stored in an isolated tank 320. The melted slag 305that passes through the heat exchanger 315 goes to a granulator 330;where in the granulator 330 are produced small particles of slag. Theparticles of slag are mixed with the molten salt; then slag and moltensalt are stirred in a tank 340. Separation of molten salt and the slagresidues is carried out by decanting or filtration 350. The aerobicmolten salt produced during the stirring process dissolves metal ionsand the ions are reduced and electrodeposited as metals layers ongraphite electrodes 360, wherein the metals are recovered from thegraphite. After electrodeposition of the metals, the molten salt isreleased of metal ions and it is deposited in a tank 370, and now it isready to be recycled. The recycled molten salt goes to the initial heatexchanger 315 to be heated again and used as a heat transfer fluid.

FIG. 4 shows a schematic diagram of an exemplary production plant system400 for extracting metal ions from ore or slag using molten salt basedupon the process and system of FIGS. 2 and 3. The plant can be scaled tovarious sizes by one of skill in the art.

In tank 405 the melted slag is separated from the ore smelter, and itpasses through a heat exchanger 410 where the molten slag providesthermal energy to the recycled molten salt dropping from shaft 475 pastthe heat exchanger 410 to tank 420. The molten slag decreases itstemperature due to the heat exchanger and goes to a granulation processwhere small particles are obtained at tank 415. All of the molten saltthat is recycled is deposited in a heat insulation tank 420 where it canbe mixed with fresh salts for recovering of the salt wasted in theprocess. From the heat insulation tank 420 is taken molten salt and itis mixed at tank 425 with the slag that comes from the granulator system415. The mixture is maintained under stirring via device 430 for sometime until it reaches the thermodynamic equilibrium. In this part of theprocess the metal ions are extracted into the molten salt.

For separation of the molten salt that contains metal ions from theresidual slag, the stirring is stopped and after waiting some time theprecipitation of the residual slag is carried out; the residual slaggoes to the bottom of the tank at 435. In the bottom of the tank at 435is a gate that is opened for decanting or filtration of the molten salt.In the separation process the residual slag is taken out using acircular arm and the molten salt passes over the slag or through afilter 440. The stirring process keeps a constant temperature by usingmolten salt that comes from the heat insulation tank.

After separating the molten salt from slag, the molten salt goes to acontainer 455 with two graphite electrodes at 450 where the metal ionsare separated from the molten salt by electrodeposition of metal on agraphite electrode. As metal forms at the graphite cathode, on the anodethe graphite will oxidize to carbon dioxide, due to anodic current andthe presence of trace water in the molten salt in contact with air. Thewater ultimately comes from the air. The container where theelectrodeposition is carried out is maintained at elevated temperature(greater than 400 degrees Celsius) using heat exchanged from the moltensalt that came from the heat insulation tank 420 at pipe opening 460.When almost all of the metal ions are separated from the molten salt byelectrodeposition, a gate is open and the metal depleted molten salt ispoured into a second heat insulation tank 470 or piped in via pipes 465.From this second insulation tank 470, the molten salt is recycled to theheat exchanger via piping to opening 475 and/or by using a mobilecontainer in order to be heated again at the heat exchanger 410.

It is recognized that the system illustrated in FIG. 4 is one exemplaryembodiment, and that one of skill in the art could readily modify theschematic to arrive at an equivalent system of a large scale facilityfor extracting metal from melted slag.

The terms “plurality” may be used throughout the specification todescribe two or more components, devices, elements, units, parameters,or the like. Unless explicitly stated, the method embodiments describedherein are not constrained to a particular order or sequence.Additionally, some of the described method embodiments or elementsthereof can occur or be performed at the same point in time.

Although various features of the present disclosure may be described inthe context of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although thevarious embodiments may be described herein in the context of separateembodiments for clarity, they may also be implemented in a singleembodiment. It is to be understood that the phraseology and terminologyemployed herein is not to be construed as limiting and are fordescriptive purpose only. It is to be understood that the details setforth herein do not construe a limitation to an application of thevarious embodiments.

1. A method of producing pure metallic copper in an electrolytic cellcontaining a molten salt electrolyte, the method comprising the stepsof: providing a vessel for containing the molten salt electrolyte at atemperature of between 500° C. and 1200° C., said vessel comprising abottom and walls extending upwardly from said bottom, wherein saidvessel further comprises an outlet configured as a drain; providing atleast one copper-containing compound; dissolving said at least onecopper-containing compound in said molten salt electrolyte; providing atleast one anode in liquid communication with said molten saltelectrolyte; providing at least one cathode in communication with saidvessel bottom; passing an electrical current through said anode and saidcathode, thereby depositing molten copper at said cathode and producinggas at said anode; removing copper deposited at said cathode through theoutlet in said vessel.
 2. The method of claim 1, wherein said vesselfurther comprises a mechanical stirrer configured to aerate said moltensalt electrolyte and any copper copper-containing compounds dissolvedtherein.
 3. The method of claim 1, wherein said vessel is composed offused quartz.
 4. The method of claim 1, wherein said anode and saidcathode are composed of graphite carbon.
 5. The method of claim 1,wherein said electrolyte comprises at least one compound selected fromthe group consisting of the halide salts of alkali metals, alkalineearth metals, and magnesium.
 6. The method of claim 1, furthercomprising the step of monitoring the electric potential of the moltensalt electrolyte using a reference electrode.
 7. A method of producingpure metals from slag obtained from the copper mining process using anelectrolytic cell containing a molten salt electrolyte, the methodcomprising the steps of: providing an extraction vessel for containing amixture of molten salt electrolyte and slag at a temperature of between1000° C. and 1200° C., wherein said extraction vessel comprises a bottomand walls extending upwardly from said bottom and is configured with amechanical stirrer to aerate the mixture of slag and molten saltelectrolyte contained in the extraction vessel, thereby causing metalions in the slag to be dissolved as metal ions in the electrolyte;wetting said slag in said molten salt electrolyte in said extractionvessel; removing metal ion-depleted slag from said extraction vessel;transferring metal ion-rich electrolyte from said extraction vessel tosaid electrodeposition vessel; providing an electrodeposition vessel inliquid communication with said extraction vessel, said electrodepositionvessel comprising: a bottom and walls extending upwardly from saidbottom, and further comprising an outlet configured as a drain; at leastone anode; at least one cathode in communication with said vessel bottomin said electrodeposition vessel; passing electrical current throughsaid anode and said cathode in said electrodeposition vessel, therebydepositing molten metal at said cathode and producing gas at said anode;removing metal deposited at said cathode through the outlet in saidvessel.
 8. The method of claim 7, wherein said vessel further comprisesa mechanical stirrer configured to aerate said molten salt electrolyteand any copper copper-containing compounds dissolved therein.
 9. Themethod of claim 7, wherein said vessel is composed of fused quartz. 10.The method of claim 7, wherein said anode and said cathode are composedof graphite carbon.
 11. The method of claim 7, wherein said electrolytecomprises at least one compound selected from the group consisting ofthe halide salts of alkali metals, alkaline earth metals, and magnesium.12. The method of claim 7, further comprising the step of monitoring theelectric potential of the molten salt electrolyte using a referenceelectrode.
 13. An electrolytic cell for the production of pure coppermetal, the electrolytic cell comprising: a molten salt electrolytehaving at least one copper-containing compound dissolved in therein; avessel for containing the molten salt electrolyte at a temperature ofbetween 500° C. and 1200° C., said vessel comprising a bottom and wallsextending upwardly from said bottom, wherein said vessel furthercomprises an outlet configured as a drain; at least one anode in liquidcommunication with said molten salt electrolyte; at least one cathode incommunication with said vessel bottom; a source of electrical current incommunication with said anode and said cathode.
 14. The electrolyticcell of claim 13, further comprising a reference electrode formonitoring the electric potential of the molten salt electrolyte. 15.The electrolytic cell of claim 13, wherein said vessel further comprisesa mechanical stirrer configured to aerate said molten salt electrolyteand any copper copper-containing compounds dissolved therein.
 16. Themethod of claim 13, wherein said vessel is composed of fused quartz. 17.The method of claim 13, wherein said anode and said cathode are composedof graphite carbon.
 18. The method of claim 13, wherein said electrolytecomprises at least one compound selected from the group consisting ofthe halide salts of alkali metals, alkaline earth metals, and magnesium.